Here's the original equation (correct me if I'm wrong):
[tex] x = \frac{w+y+z}{7} [/tex]
To solve for y, we need to isolate it. So, let's solve it:
[tex] x*7 = (\frac{w+y+z}{7}) * 7 [/tex]
[tex] 7x = w+y+z [/tex]
Now, let's subtract w and z, and our final answer is:
y = 7x-w-z